A conventional microscope enables an operator to view magnified images of minute features on a sample otherwise invisible to the human eye. Because of this, conventional microscopes have been widely used in universities, in research institutes, and in many industries. A conventional microscope, however, has important limitations. For example, it only provides a two-dimensional (2-D) image of a sample while in the real world a majority of samples are 3-D in nature.
Various improvements have been made over the years to achieve 3-D viewing and 3-D imaging with optical microscopes. Costales in U.S. Pat. No. 6,275,335 discloses a stereomicroscope using various polarizing optical components to achieve a stereoscopic effect in the image. Although Costales' microscope produces a perception of depth, it cannot provide quantitative measurement of the depth dimension.
Kino in U.S. Pat. No. 5,022,743 proposes a confocal microscope utilizing a spinning Nipkow disc. Sheppard in U.S. Pat. No. 4,198,571 discloses a confocal microscope based on laser scanning. Although a confocal microscope is able to generate a 3-D image and provide quantitative depth measurement, it is expensive to build and relatively complex to maintain and operate. In addition, if one already bought a conventional microscope, it is not easy and in many cases impossible to turned his microscope into a confocal microscope.
Sieckmann in U.S. Appl. No. 2004/0257360A1 proposes a method of creating 3-D images of a sample by analyzing a stack of images of the sample taken at various focus positions. Although it is cost effective to implement such a method, it only works on samples with contrasting features. In short, Sieckmann's method fails to generate a reliable and accurate 3-D image of a sample with little or no contrast.
Morgan in U.S. Pat. No. 5,381,236 proposes an optical range sensor that is capable of sensing the depth profile of a plain surface by actively projecting a pattern of light onto the target object. Although Morgan's sensor measures the 3-D profile of a sample, it does not combine the 3-D profile with the intensity or color information of the sample. As a result, his sensor does not yield a 3-D image. In addition, the pattern of light in Morgan's sensor is always superimposed on the sample surface, and thus interferes with the true features of the sample surface being captured by a camera.
Accordingly, there is a need for a 3-D optical microscope that is relatively low cost to build and easy to operate; a method that can be easily deployed to turn a conventional microscope into a 3-D optical microscope; and a 3-D imaging method that works on all samples regardless of their feature contrast.